I’m going to teach you about what an image’s dots-per-inch (DPI) is for, because I want to save you from suffering the way I have.

Why Every Designer Needs to Know DPI

What kind of pain and suffering can I save you?

I once spent three hours redoing work on a 8-foot by 3-foot photo-collage banner because the person who started the file didn’t know how DPI and resolution worked. The photos in the collage weren’t saved at a high enough resolution to print at larger than a few inches each, and there weren’t nearly enough of them to span eight feet across.

It doesn’t even have to be someone else’s mistake. I’ve done this to myself: starting projects at a low resolution and then realizing later that it can’t be printed at the size I needed.

What is DPI?

Let’s take some time to clear up some terms.

DPI stands for Dots Per Inch, and it’s a specification for a printer, meaning how many physical dots of ink will it print in a full square inch. Your home inkjet or laser printer will do alright at 200 dots per inch, but a professional printers typically won’t print at less than 300dpi or higher. That’s so that when you look at the final print-out, the image comes out crisp. If you use fewer dots, the image will come out blurry or seem pixelated.

For smooth detail, you want lots of small dots, tightly packed together, so the viewer can’t tell where where one dot ends and the next begins.

Here’s a visual demonstration of what I mean.

PPI stands for Pixels Per Inch, which refers to how many squares of colored light a screen fits in one square inch. Standard displays have 72 pixels per inch. Some monitors have 90ppi, and those in Apple’s “Retina” category can have hundreds of pixels per inch. If you’re curious, you can easily find out the PPI of your screen at DPI Love.

Checking an Image’s DPI

To find out an image’s DPI, right-click on the file name > Properties > Details. You’ll see the DPI in the Image section, labelled Horizontal Resolution and Vertical Resolution.

Change DPI in Photoshop

To change an image’s DPI in Photoshop, go to Image > Image Size. Now this is very important: Uncheck “Resample Image” at the bottom of the window. If you don’t, Photoshop will simply upsample the image, meaning it’s adding pixels without adding detail.

The screencapture above is from Photoshop CS2, but the instructions work exactly the same for higher versions of Photoshop, too. If you’ve done this correctly, you’ll notice the file size of the image doesn’t change. Only the end-printout will – you’ll see the same pixels, packed closer together.

Change DPI in GIMP

If you’re editing your image in GIMP, you can change the DPI by going opening the Image menu > Print Size. Then, enter the resolution you require for the x-axis and y-axis, and click OK. Unlike in Photoshop, you won’t need to worry about upsampling.

You’ll notice the print size will change, because changing how many dots per inch you want printed will mean you’re fitting more pixels into the same amount of space, shrinking the result.

If you keep the chain symbol linked, it will automatically change the y-axis to scale. Un-link the chain if you want to change the horizontal and vertical DPI independently from each other for some reason.

Change DPI Free Online

If you’re in a pinch and you don’t have your graphics program of choice on hand, you can always change the DPI of an image with Convert Town’s DPI-changing web-app, for free online.

All you have to do is input the DPI you need the image changed to, drag-and-drop the file to upload it, and wait. When it’s done converting, it should automatically download it to your default download folder.

Learning More

There you have it: three of the best free and easy ways to change a graphic’s DPI. It’s not hard to do but trust me: it will save you headache if you get it right before you start your next print design.

I don't often comment, but your post on changing the dpi was very helpful to me. I am doing some senior class photos for my daughter and it mentioned needed 300 dpi, but was set for 72. I almost came to the conclusion that photos I had taken were worthless, til I read your post.

Hello,
I'm having a problem that kinda concerns this and something else simultaneously. I have an image that I may want to make prints of. I have both PNG and PDF copies of it, it's been converted into CMYK, and it's currently at 500 dpi, which if I understand properly is well above the standard dpi of 300 that people tend to use for printing. That's fine, but my real issue is that the image itself is rather small (a little less than 8in x 10in), and I wanted to make it at least a little bit bigger before printing it. Is this doable while still keeping the DPI at or above 300?

wow someone who knows the difference between ink drops, LPI, pixels, the one thing that is not mentioned in this article that needs to go in is
For printing, retain the ORIGINAL pixel dimensions changing the resolution from say 4000 x 2000ppi to 36000 x 18000ppi makes the image softer, reduces the corrections you can make in photoshop or their effectiveness and increases processing time. IT DOES NOT HELP TO INCREASE THE FILE SIZE, IT ACTUALLY DEGRADES THE IMAGE.
If you work in large format, use a higher quality camera, a canon 5dsr (50megapixel) or phase one medium format

Changing density doesn't change image itself, but image metadata. So if changing ppi degrades your image, changes anything in image, you should consider using better tools. I think you have mistaken print size with image size. Still, upscaling image doesn't mean it always would degrade image. What degrading could be in x2 method?

And as for rather powerusers - you can script some command line tool. Like batch file. Let me present example for Windows for JPEG (!). You need exiftool (open source). Rename the original file to exiftool.exe and put it in the Windows directory (or to other directory in your %PATH%). Create new file with extension ".bat". Let me explain how it works. You need to drag file and drop it on the newly crated file. At first it gives you name of the file (I like such feedback to be sure I modify correct file), then it asks you about new dimensions. Warning: this code assumes that units are inches (the are rarely different), that you wrote proper number, not gibberish and that file if JPEG (in last case it will just fail, in second it could fail). Now, if author's willing to add my code, I'll be glad to make it better (including choosing from menu standard values, using last given value and processing many files/directories). So if the author wants it, please write to my mail and I'll send you code. So the simple version of code is:
@echo off
setlocal
echo You are about to process image "%~nx1".
for /f %%i in ('exiftool -s -s -s -jfif:Xresolution "%~1"') do set currDPI=%%i
set /p newDPI="Enter new resolution (current: %currDPI% dpi): "
exiftool -P -overwrite_original -jfif:Xresolution=%newDPI% -jfif:Yresolution=%newDPI% %1
endlocal
pause

I am using Window 10 but i cannot vizualise the number of DPI in the case of the files in BITMAP format. I followed the procedure described on this web page ("Checking an image's DPI") but the number of DPI is not displayed. Please could you help ?

Jessica, thank you! I'm an iPhone Photographer but my images (72dpi) are often requested for print publications. I've known the images can be 'inter-something' so they're print ready but never known how! You're article has nailed it - and delightfully, easy to follow. Thank you again! xxXxx

Awesome informative well written article! Thank you so much for sharing this information! I play around with graphics and saw problems due to DPI even on personal photos Example you have an old Polaroid photo you want to copy and print because they have a tendency to deteriorate Problem go to try to print and it looks horrible due to the DPI being too low So to whoever wrote this thanks "You Rock"